Probability & Heredity A number that describes how likely it is that an event will occur. The laws of probability predict was is likely to occur, not necessarily what will occur. Probability is written as The number of ways of getting a particular outcome to the total number of possible outcomes. Can be expressed as a ratio, fraction, decimal or percent Ex.) Getting heads when flipping a coin 1 to 2, ½, .50, or 50%

Independent versus Dependent events Independent event An event in which the outcome or the likelihood of an outcome is not affected by a 2nd event happening. Ex.) Landing on heads after tossing a coin AND rolling a 5 on a single 6-sided die. Ex.) Choosing a marble from a jar AND landing on heads after tossing a coin. Dependent event An event in which the outcome or the likelihood of an outcome is affected by the outcome of the 1st event. Ex.) Picking 3 Aces in a row from a deck of cards without replacing the cards.

Punnett square Developed by Reginald Punnett a British geneticist. A chart that shows all the possible combinations of alleles that can result from a genetic cross for a specific trait. Also called a monohybrid cross when trying to determine the possible allele combinations when dealing with 1 trait or dihybrid cross when dealing with 2 traits.

Completing a Punnett Square. Start by drawing a box & dividing it into 4 squares. Write the male parent’s alleles along the top of the square & the female parent’s alleles along the left side. R r

Copy the male parent’s alleles into the boxes beneath them. Copy the female parent’s alleles into the boxes to their right. R r RR Rr rr

R r RR Rr rr In a Punnett square, each square is equally to ¼ or 25%. The completed Punnett square shows all the possible allele combinations for the offspring. In a Punnett square, each square is equally to ¼ or 25%. To determine the total probability of a particular outcome determine the number of times that outcome appears in the Punnett square & multiply by 25% or ¼. Ex.) Rr = 2 squares  2 x 25% 50% or ½. R r RR Rr rr

Genotype An organisms specific allele combination for a trait Seed color: YY, Yy, or yy Seed shape: RR, Rr, rr Categories of genotypes Heterozygous Having 2 different alleles for a trait Also known as hybrids Yy or Rr Homozygous Having the same 2 alleles for a trait Also known as purebreds YY or yy; RR or rr

Phenotype The physical appearance or visible traits. In human genetics heterozygotes; those who have a dominant and a recessive allele are called carriers. This means they are carrying a recessive allele without expressing it physically. Genotypes Phenotypes YY Homozygous Yellow Yy Heterozygous yy Green

Codominance or “Incomplete dominance” The alleles are neither dominant or recessive as a result both alleles are expressed in the offspring. Ex.) Roan cattle or Appaloosa horses Ex.) Hazel or dual colored eyes in humans & animals Huskies  1 white & 1 blue eye or 1 blue & 1 brown eye Both alleles for the trait are written as superscripts for the trait. Ex.) Feathers  FBFW Black & White Feathers Ex.) Eye color  EBEg Hazel eyes